Coal has been extensively used as a fuel for thermal power generation and boilers or a raw material for chemicals. As one of the environmental measures, there has been a strong demand for the development of a technique for efficiently removing ash in coal. For example, in a high-efficiency hybrid power system using gas turbine combustion, an attempt has been made to use ash-free coal, in which ash is removed, as an alternative fuel to a liquid fuel, such as LNG.
In a known method as a method for producing ash-free coal (for example, PTL 1), a slurry prepared by mixing coal and a solvent is heated to extract a coal component soluble in the solvent (hereinafter, referred to as a “soluble component in the solvent). A supernatant liquid containing the soluble component in the solvent and a solid-content concentrated liquid containing a coal component, such as ash, which is insoluble in the solvent (hereinafter, referred to as an “insoluble component in the solvent”) are separated. Separating the solvent from the supernatant liquid provides ash-free coal.
In addition, as a technique for efficiently separating a slurry into a solid-content concentrated liquid and a supernatant liquid, a gravitational settling tank using a gravitational settling method has been known (for example, PTLs 2 and 3).
In the gravitational settling tank described in PTLs 2 and 3, however, the opening of the outlet of a slurry supply pipe faces downward, and the slurry gushes from the outlet. The flow of the slurry concentrates at a point, thus disadvantageously agitating the solid-content concentrated liquid settled in the lower portion of the gravitational settling tank.
As a technique attempting to solve the foregoing problem, a gravitational settling tank or the like having the effect of dispersing a slurry flow by arranging a plate member below an outlet of a slurry supply pipe has been reported.